1. Field of the Invention
The invention relates to an apparatus and method for measuring a longitudinal modulus of elasticity of a fiber to be used for composite materials, such as Nickaron, Tyrano, SCS-6 and Nextel.
2. Description of the Related Art
These days, carbon fibers are widely used to reinforce polymer matrix composites (PMCs). In addition to PMCs, and metal matrix composites (MMCs) reinforced by continuous fibers, ceramic matrix composites (CMCs) have been researched and developed by using ceramic continuous fibers. In particular, continuous ceramic fiber such as Nickaron, Tyrano, SCS-6 and Nextel have been developed as reinforcing fibers for CMCs.
A longitudinal modulus of elasticity or Young's modulus of those continuous fibers having high stiffness has been conventionally measured in accordance with, for instance, a carbon fiber testing method defined in JIS-R7601. This method includes the steps of taking a single fiber out of samples one by one, adhering the single fiber at its opposite ends onto a sheet having an opening, recording a load-elongation curve by means of a tensile tester, and calculating the longitudinal modulus of elasticity E based on the gradient of the load-elongation curve in accordance with an appropriate equation.
The above mentioned conventional method is simple in principle, and hence can be applied to a wide range of fibers, but has problems that measurement procedure is complicated and that actual measurement takes much time. It is quite important to order to use these fibers in a composite material to measure the longitudinal modulus of elasticity E at a high temperature. However, it is quite difficult to hold a fiber at a high temperature, and in addition, large-scaled equipments and complicated, time-consuming measurement procedure are required to obtain a load-elongation curve at a high temperature in the above mentioned conventional method. Furthermore, the conventional method has another problem that since many test fibers are consumed for obtaining test data, a lot of test fibers have to be prepared for each of the test temperatures.
In particular, when fibers are used for composite material, the above mentioned conventional method has problems as follows.
First, rupture strain of the ceramic fibers is in the range of about 0.5 to 2 %, which are remarkably smaller than those of the other fibers. Thus, since a small misalignment in the fiber arrangement and a small difference in elongation among the fibers exert great influence on the measurement, and furthermore since the fiber is broken with a quite small load, it is quite difficult or almost impossible to exactly measure the longitudinal modulus of elasticity E of the fiber.
Second, since the fibers are brittle, they are likely to be broken at a portion at which they are grasped by a tensile tester during carrying out a tensile test. Fibers are not likely to fracture within a gauge length in which rupture of fibers is expected to occur.